In recent years, for example, HDMI® is becoming widespread as a communication interface wherein a digital television signal, i.e., the pixel data of an uncompressed (baseband) image, and audio data accompanying the image thereof are transmitted from, e.g., a DVD (Digital Versatile Disc) recorder, set top box, or other AV (Audio Visual) source to a television receiver, a projector, or other display device at high speed.
With regard to HDMI®, a TMDS (Transition Minimized Differential Signaling) channel for transmitting pixel data and audio data from an HDMI® source to an HDMI® sink in one direction at high speed, a CEC line (Consumer Electronics Control Line) for executing two-way communication between an HDMI® source and an HDMI® sink, and so forth are stipulated in the HDMI standard.
For example, such as shown in FIG. 1, a digital television receiver 11, and an AV amplifier 12 are connected with an HDMI cable 13 conforming to HDMI®, thereby enabling the high-speed transmission of pixel data and audio data.
In FIG. 1, a digital television receiver 11, an AV amplifier 12, and a playback device 14 are installed in a living room situated to the left side in the drawing of a user's home, and between the digital television receiver 11 and the AV amplifier 12, and between the AV amplifier 12 and the playback device 14 are connected with an HDMI® cable 13, and an HDMI® cable 15.
Also, a hub 16 is installed in the living room, and the television receiver 11 and the playback device 14 are connected to the hub 16 using a LAN (Local Area Network) cable 17 and a LAN cable 18. Further, in the drawing, a digital television receiver 19 is installed in a bedroom situated to the right side of the living room, and the digital television receiver 19 is connected to the hub 16 via a LAN cable 20.
For example, in the case that a content recorded in the playback device 14 is played, and an image is displayed on the digital television receiver 11, the playback device 14 decodes the pixel data and audio data for playing the content, and supplies the uncompressed pixel data and audio data obtained as a result thereof to the digital television receiver 11 via the HDMI® cable 15, AV amplifier 12, and HDMI® cable 13. Subsequently, the digital television receiver 11 displays an image, or outputs audio based on the pixel data and audio data supplied from the playback device 14.
Also, in the case that a content recorded in the playback device 14 is played, and an image is displayed on the digital television receiver 11 and the digital television receiver 19 simultaneously, the playback device supplies the compressed pixel data and audio data for playing the content to the digital television receiver 11 via the LAN cable 18, hub 16, and LAN cable 17, and also supplies those to the digital television receiver 19 via the LAN cable 18, hub 16, and LAN cable 20.
Subsequently, the digital television receiver 11 and digital television receiver 19 decode the pixel data and audio data supplied from the playback device 14, and displays an image or outputs audio based on the uncompressed pixel data and audio data obtained as a result thereof.
Further, in the case that the digital television receiver 11 has received pixel data and audio data for playing a program on air on television, in the event that the received audio data is, for example, 5.1-channel surround audio data or the like, and the digital television receiver 11 has difficulty in decoding the received audio data, the television receiver 11 converts the audio data into an optical signal, and transmits this to the AV amplifier 12.
The AV amplifier 12 receives the optical signal transmitted from the digital television receiver 11 to subject this to photoelectric conversion, and decodes the audio data thus obtained. Subsequently, the AV amplifier 12 amplifies the decoded uncompressed audio data as appropriate, and plays the audio using a surround speaker connected to the AV amplifier 12. Thus, the digital television receiver 11 decodes the received pixel data, displays the image based on the decoded pixel data, and plays the 5.1-channel surround program by outputting the audio using the AV amplifier 12 based on the audio data supplied to the AV amplifier 12.
Incidentally, with regard to HDMI®, a device has been proposed wherein when transmitting pixel data and audio data from an HDMI® source to an HDMI® sink, discarded data is muted by turning on/off transmission of data (e.g., see Patent Document 1).
Further, with regard to HDMI®, a device has been proposed wherein, of multiple HDMI® sinks, pixel data and audio data can be output to a desired HDMI® sink without switching a cable for connecting an HDMI® source and an HDMI® sink by switching a terminal for outputting pixel data and audio data using a changeover switch (e.g., see Patent Document 2).    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-57714    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-19948